Re: amp build - twisting wires

guitarPsych wrote:
What about the two wires from the output transformer that go to the output jacks, one for 8 ohm and one for 4 ohm. Should they be twisted together?

Stephen Cowell wrote:

"Phil S." <psymonds_no_spam@xxxxxxxxxxx> wrote in message
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"guitarPsych" <none@xxxxxxxx> wrote in message
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Is there a purpose to twisting wires from the power transformer, FIL,
etc., or is that just a cosmetic thing? If so, what is the purpose...
what happens if you don't?


On an AC circuit, twisted pair is the tried and true method of cancelling
hum. Filaments are usually AC. The primary and secondaries on the power
tranny are AC between the tranny and the rectifier, so all those should be
twisted pair. The runs from the output plates to the output tranny and


from

the OT to the speaker are also AC. All these should be twisted. There


may

be a bit of other AC running inside the amp, but nothing comes to mind.
These are the essential ones. We don't do it because it looks neat.
Everything we do has a reason. This was a good question.

One other thing... to separate AC from DC, typically we run the DC on the
floor of the chassis and put the AC wires up in the air. This is also


meant

to kill hum. All this is part of lead dress and proper wire placement.
Sometimes, we need to find the proper placement with a chopstick on a live
chassis.



It's not because it's an AC circuit... it's because it's a *balanced*
circuit,
which means that both conductors are co-equal carriers of 180degrees
out-of-phase signal or power. It's the combination of proximity (the twist
guarantees this, it's not because of any special 'spin' property) and phase
cancellation that limits the radiation from the twisted pair. Note that
this
does not shield the pair itself from common-mode noise (noise that appears
on both wires at the same time, *in phase*).

Normal lead dress would have the big signal wires (plates and cathodes)
close
to the chassis and the grid wires (small signal, high impedance) up in the
air,
but far away from your twisted pair filament signals. You can also twist
the
OT plate wires together, as well as the PI outputs if long enough... works
for
any balanced signal.
__
Steve
.


hope you're joking....
.

Relevant Pages

  • Re: amp build - twisting wires
    ... twisted pair is the tried and true method of cancelling ... floor of the chassis and put the AC wires up in the air. ... It's not because it's an AC circuit... ... but far away from your twisted pair filament signals. ...
    (alt.guitar.amps)
  • Re: amp build - twisting wires
    ... What about the two wires from the output transformer that go to the output jacks, one for 8 ohm and one for 4 ohm. ... cancellation that limits the radiation from the twisted pair. ... but far away from your twisted pair filament signals. ...
    (alt.guitar.amps)
  • Re: amp build - twisting wires
    ... twisted pair is the tried and true method of cancelling ... floor of the chassis and put the AC wires up in the air. ... It's not because it's an AC circuit... ... but far away from your twisted pair filament signals. ...
    (alt.guitar.amps)
  • Re: Twisted Pairs - how tightly should I be twisting the wire?
    ... I was just planning on twisting two 18 AWG ... twisted pair seemed like a decent idea as it's ... twists of wire per foot. ... wires, etc. that need to be twisted into a twisted pair before they ...
    (alt.guitar.amps)
  • Re: Twisted Pairs - how tightly should I be twisting the wire?
    ...  I was just planning on twisting two 18 AWG ... twisted pair seemed like a decent idea as it's ... twists of wire per foot. ... wires, etc. that need to be twisted into a twisted pair before they ...
    (alt.guitar.amps)
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